Vice President Biden speaks at the Chesterfield Country Fairgrounds on Sept. 25 in Chesterfield, Va. / Win McNamee, Getty Images

by Gregory Korte and Aamer Madhani, USA TODAY

by Gregory Korte and Aamer Madhani, USA TODAY

WASHINGTON -- Both sides expect Vice President Biden to be on the offensive when he shares a Kentucky stage with GOP candidate Rep. Paul Ryan in the one and only televised vice presidential debate Thursday night.

"He's got to go right at Ryan and shake him from the very beginning," said Chris Kofinis, a Democratic strategist. "He's got to put him on the defensive from the get-go."

Ryan himself told Detroit radio station WJR on Monday that he expects Biden to come at him like a "cannonball."

As Biden prepared for Thursday's debate, the pressure was on him to stop, or at least slow, the momentum that the Mitt Romney-Ryan ticket has enjoyed since last week's presidential debate. Even President Obama has acknowledged he had an off-night at the debate, allowing Romney to seize the initiative.

"I think it's fair to say I was just too polite," the president told radio host Tom Joyner on Wednesday. "Because, you know, it's hard to sometimes just keep on saying, 'And what you're saying isn't true."

Since then, Romney has rebounded in the polls - leading Obama by 1 percentage point in the national polling RealClearPolitics average for the first time in a year.

"Some of what Romney said in terms of changing positions, denying things he believed in before, or his lack of specificity â?¦ I think it is important that we make sure it is challenged in a way that it wasn't challenged last week," said Delaware Gov. Jack Markell, a Democrat who is a surrogate for the Obama campaign.

Rep.Chris Van Hollen, D-Md., who has been playing the role of GOP vice presidential nominee during debate preparation with Biden, charged that "it is an open question if Congressman Ryan will lay out anything that stands the scrutiny of the fact checkers."

Ryan spokesman Michael Steel said the Republican ticket expects that line of attack, and is well-prepared to defend the facts and statistics that Ryan -- wonkish by reputation -- will lay out.

"There's always an emphasis on making sure everything is factually correct," Steel said. "This is the kind of attack you expect from politicians who can't run on their record."

"I think what you saw last week is an Obama campaign that's uninspiring. His campaign doesn't have a message," said Republican National Committee Chairman Reince Priebus. "I like where we're sitting right now in the campaign. I don't think anyone's looking for a walk-off grand slam."

In the well-worn tradition of managing expectations, both sides portrayed their opponent as a worthy debater.

Markell said Ryan is "a very bright guy and he has communicated very effectively what he believes." Priebus, exaggerating slightly, told USA TODAY that Biden has "150 years" of experience. "To somehow believe he's going to be a gaffe-machine at the debates, that's not going to happen."

One indication of the importance of the debate is the amount of time each candidate has spent preparing. Ryan began shortly after the Republican convention helping to write and edit the policy binders, Steel said.

There has been at least eight or nine days spent in practice sessions, Steel said: three days in Virginia and a day and a half in Florida last month; two days in Washington, D.C., and one in Wisconsin with sparring partner Ted Olsen last week; and Ryan plans to spend another day preparing Thursday in Kentucky, home to debate host Centre College in Danville.

Biden huddled over three days in his hometown of Wilmington, Del., with longtime adviser Ted Kauffman, his chief of staff Ron Klain, and Obama campaign adviser David Axelrod ahead of the debate. The group reviewed videos of old Ryan speeches while running through mock debates with Van Hollen standing in as Ryan.

Vice presidential debates are usually proxy wars for the men at the top of the ticket, said Joel Goldstein, a law professor at St. Louis University and an expert on the vice presidency. "If you find yourself spending a lot of time talking about the person across the stage from you, you're probably making a mistake," he said.